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Sesamoid bone of great toe

The sesamoid bones of the great toe are two small, oval-shaped ossicles embedded within the tendons of the flexor hallucis brevis beneath the head of the first metatarsal. They are the medial (tibial) sesamoid and lateral (fibular) sesamoid, which lie on either side of the flexor hallucis longus (FHL) tendon.

These sesamoids act as pulleys, increasing the mechanical advantage of the FHB tendons during toe flexion, reducing friction, and protecting the FHL tendon as it passes between them. They also play a vital role in weight distribution and stabilization of the first metatarsophalangeal (MTP) joint during push-off in gait.

Synonyms

  • Hallucal sesamoid bones

  • First metatarsal sesamoids

  • Tibial and fibular sesamoids

Number and Variations

  • Normal configuration: Two sesamoids (medial and lateral)

  • Medial (tibial) sesamoid: Larger and more medial, more commonly affected by pathology

  • Lateral (fibular) sesamoid: Smaller and more lateral

  • Variants:

    • Bipartite sesamoid: A developmental variant (usually medial) with a well-corticated cleft between parts

    • Accessory sesamoid: Rare, may occur near the intersesamoidal ridge

Location and Relations

  • Superiorly: Head of the first metatarsal

  • Inferiorly: Plantar skin and subcutaneous tissue of forefoot

  • Medially: Medial belly and tendon of flexor hallucis brevis

  • Laterally: Lateral belly and tendon of flexor hallucis brevis

  • Centrally: Tendon of flexor hallucis longus passing between them

  • Posteriorly: Medial plantar nerve and artery branches

  • Anteriorly: Base of the proximal phalanx of the hallux

Attachments

  • Embedded tendons: Flexor hallucis brevis (medial and lateral heads)

  • Ligamentous connections:

    • Inter-sesamoidal ligament (connects both sesamoids)

    • Medial and lateral metatarsosesamoid ligaments (to first metatarsal head)

    • Phalangeosesamoid ligaments (to base of proximal phalanx)

  • These attachments stabilize the first MTP joint and prevent sesamoid displacement

Arterial Supply

  • Branches of the medial plantar artery (from posterior tibial artery)

  • Contributions from first plantar metatarsal artery

Venous Drainage

  • Plantar venous plexus → medial plantar vein → posterior tibial vein

Function

  • Mechanical advantage: Acts as pulleys to improve leverage of FHB during hallux flexion

  • Load distribution: Absorbs compressive forces at the first metatarsal head during gait

  • Friction reduction: Protects the FHL tendon as it glides between sesamoids

  • Joint stabilization: Maintains alignment of the first MTP joint during push-off

  • Shock absorption: Prevents direct pressure on the metatarsal head

Clinical Significance

  • Sesamoiditis: Inflammation and pain beneath the first MTP joint from repetitive stress

  • Stress fracture: Common in runners and dancers; medial sesamoid most affected

  • Bipartite sesamoid: May be mistaken for a fracture; typically well-corticated and smooth margins

  • Osteonecrosis (Renander’s disease): Avascular necrosis of the medial sesamoid causing chronic forefoot pain

  • Dislocation or subluxation: May occur with hallux valgus or trauma

  • Post-surgical relevance: Important in hallux valgus correction, sesamoidectomy, and bunion procedures

MRI Appearance

  • T1-weighted images:

    • Normal bone: Intermediate signal; cortex appears dark, marrow slightly brighter

    • Cancellous bone marrow: Intermediate signal

    • FHB tendons: Low signal crossing plantar to the sesamoids

    • Pathology:

      • Fracture: low-signal line through sesamoid with surrounding intermediate marrow edema

      • Avascular necrosis: diffusely low signal intensity

  • T2-weighted images:

    • Normal sesamoid: Intermediate signal; cortex appears dark, marrow slightly brighter

    • Muscle and tendons: Low signal intensity

    • Edema or fracture: Hyperintense marrow or soft tissue changes surrounding sesamoid

    • Bipartite sesamoid: Smooth, well-corticated cleft, no surrounding edema

  • STIR:

    • Normal sesamoid and adjacent muscle: Intermediate-to-dark signal

    • Inflammation or fracture: Bright hyperintense signal in marrow or adjacent soft tissue

    • Useful for early detection of stress reactions, edema, or sesamoiditis

  • Proton Density Fat-Saturated (PD FS):

    • Normal: Intermediate-to-dark signal intensity

    • Pathology: Bright hyperintense marrow or peritendinous signal indicating edema or fracture

    • Sesamoiditis: Diffuse hyperintensity within and around the sesamoid bones

    • Avascular necrosis: Central low signal with peripheral bright rim of reactive edema

  • T1 Fat-Sat Post-Contrast:

    • Normal: Mild, uniform marrow enhancement

    • Inflammatory lesions: Marked enhancement around sesamoids (peritendinous or capsular)

    • Avascular necrosis: Peripheral rim enhancement with central non-enhancing necrotic area

    • Fracture: Enhancing surrounding soft tissue and bone marrow edema

CT Appearance

Non-Contrast CT:

  • Normal sesamoid: Small oval dense ossicle beneath first metatarsal head with smooth cortical margins

  • Bipartite sesamoid: Two well-corticated fragments with a narrow gap, typically medial

  • Fracture: Sharp, irregular lucent line through bone, non-corticated margins, often with displacement

  • Sclerosis or cortical irregularity: Seen in chronic sesamoiditis or avascular necrosis

  • Surrounding soft-tissue swelling may indicate inflammation or trauma

Post-Contrast CT (standard):

  • Normal: Cortical bone remains non-enhancing

  • Inflamed sesamoid region: Peri-sesamoid soft-tissue and joint capsule enhancement

  • Postoperative or chronic cases: Detects calcification, ossification, or fibrosis

MRI image

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MRI image

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MRI image

sesamoid bone great toecoronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

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